The present invention relates to a clamping device that is capable of clamping a workpiece, particularly a component of automobiles, agricultural machines and implements and the like, in a compressed or tensioned state.
A known clamping device for use in fixing a workpiece, is disclosed in Japanese patent publication No. 54-3280. FIG. 5 shows a schematic view of such a clamping device.
In FIG. 5, numeral 1 denotes a base member 1, which has a fastening surface portion 1a and a pair of upright wall portions 1b. On the base member 1, a clamp arm 2 and an operating lever 3 are pivotally mounted via corresponding shafts 4 and 5, respectively.
The operating lever 3 is formed with a toggle mechanism T that is interlocked with the lever. Specifically, a link member 8 is mounted on part of the length of the operating lever 3 so that the link member is able to pivot around a shaft 7, and a lower end portion of this link member 8 is linked with part of the length of the clamp arm 2 via a shaft 9 that operates as an output member.
Numeral 8a denotes an engagement portion for restraining the link member 8 from unstrainedly pivoting around the shaft 9.
Numeral 10 denotes a pressing member mounted on the clamp arm 2 so that the pressing member is adjustable for its vertical position.
The above-mentioned clamping device is used with the fastening surface portion 1a of the base member 1 fastened to an appropriate base, and is operated in the following manner.
That is, when fixing a workpiece, the operating lever 3 is initially tilted in the direction of arrow f around the shaft 5, whereby the clamp arm 2 is lifted up via the toggle mechanism T. In this state, the workpiece is placed on a support base provided below the pressing member 10.
Next, the operating lever 3 is raised up with a relatively small operating force in the direction of f1 opposite to the previous direction f. By this operation, the clamp arm 2 is lowered and the pressing member 10 abuts against the workpiece. At this point of time, the operating lever 3 will not be displaced any further by a small operating force.
Subsequently, a greater operating force is applied to the operating lever 3 in the same direction, thereby displacing the lever in the same direction. By this operation, the output member 9 strongly pushes down the clamp arm 2 by the toggle effect of the toggle mechanism T, and the pressing member 10 strongly presses the workpiece against the support base.
According to the aforementioned prior art clamping device, the toggle effect provided by the toggle mechanism is significantly reduced even when the height of the workpiece to be fixed is varied slightly (about several millimeters), so that the workpiece cannot be firmly fixed.
If abrasion occurs in any contact portion of the members due to repetitive use or in a similar case, then the capability of fixing the workpiece is sharply reduced similar to the case where the height of the workpiece is reduced unless a correlation with the workpiece is corrected.
In order to cope with such a situation, it is required to frequently execute vertical position adjustment of the pressing member 10 relative to the workpiece, and this becomes a factor for which impairs the work efficiency.